1. Field of the Invention
The present invention relates to a fluorescent x-ray quantitative analysis apparatus in which primary X-rays can be applied to a sample to enable a quantitative analysis of the sample on the basis of secondary X-rays emitted from the sample and, more particularly, to vary the conditions in which readings are taken, and determining the concentrations of elements based on a plurality of readings.
2. Description of Related Art
Elements in a sample have been quantitatively determined by the use of an energy dispersive X-ray fluorescent analyzer in the prior art. The fluorescent X-rays of elements heavier than Na (sodium) can usually be measured at the same time. The intensities of these fluorescent X-rays are proportional to concentrations of the respective elements in a first approximation, but the results can be greatly influence by coexisting elements in the sample due to absorption and secondary excitation effects.
As a result, the intensities of the respective fluorescent X-rays are expressed by a function of the concentrations of all the elements that are existing in a sample that is measured. This function can be theoretically calculated, and a comparison with an actual measured intensity can be conducted over a number of times equal to the number of elements in the sample. This method, in which a plurality of comparison equations or expressions are solved, as simultaneous equations, is called the fundamental parameter method.
In a conventional fluorescent X-ray quantitative determination, measurement conditions are set, such as the magnitude of a voltage (X-ray tube voltage), which is applied between a filament and a target in an X-ray tube, the particular material of a primary X-ray filter and a particular thickness is determined, and whether the X-ray beam will pass through a vacuum or air, is set. The sample is then measured under these fixed conditions, and the simultaneous equations are then set up on the basis of the intensities of the fluorescent X-rays obtained at that time. The simultaneous equations are then resolved by the use of, for example, the fundamental parameter method, to determine the concentrations of elements contained in the sample, as shown in FIG. 4. FIG. 4 sets forth the process steps in such a conventional method.
A disadvantage, however, has occurred if the measuring conditions that are set for the measurement of light elements are utilized for a sample containing elements having separate atomic numbers in mixture, since the sensitivity for heavy elements is substantially lowered. Conversely, if the measurement conditions are set to be suitable for the measurement of heavy elements, then the sensitivity for light elements is lowered, and the accuracy of the measurement will deteriorate.
As can be appreciated, this field is still looking for an optimum method of measuring multiple elements in a sample.